HMD (head mounted display) means a display device capable of directly showing an image or video in front of user's eyes by being mounted on a head or eye part. For example of the HMD, there is a see-through type HMD. And, the see-through type HMD is advantageous in implementing a virtual (imaginary) image of a large screen greater than a real panel size by enlarging an image displayed on a display panel (e.g., LCD, DMD, LCoS, OLED, etc.) through optical lenses.
However, since most of the input mechanisms of a related art HMD are very slow and inconvenient for a user, they cause a problem of failing to provide an efficient input tool to a user accustomed to a smartphone and the like. Therefore, the demand for an input mechanism of a new type is increasingly rising to solve the problem of the very inconvenient input mechanism of the HMD.
Meanwhile, a related art mobile device (e.g., a smartphone) has a problem that a user has to repeat a touch input for enlarging and reducing a specific portion of a screen due to a limited display size. Of course, a display size of a mobile device tends to increase. Yet, in aspect of mobility of a mobile device, there is a technical limitation put on increasing a screen size unlimitedly.